Footage has flooded YouTube from locations as varied as British Columbia in Canada, Allen in Texas and Queensland in Australia.

The sound, like something from Hollywood movies The War of the Worlds or Close Encounters of the Third Kind starts without warning and has people transfixed in the street as it continues.

And even the experts can't tell if it's aliens, God, the Earth or something else unknown.

Earlier this month a couple shot a clip in Germany where a child can be seen standing stock-still as it occurs.

Kimberly Wookey from British Columbia in Canada wrote on YouTube: “This is the second time I personally have heard these sounds here in Terrace, BC, Canada.

"On the morning of August 29th 2013 at approx. 7:30am I was awoken by these sounds.

"I shot out of bed and ran looking for a camera to try to capture them with. Came out into the living room to find my seven-year-old son awake and scared wondering what was going on.

"Checking my Facebook I noticed a lot of locals had heard the same sounds again but this time it was far more widespread. "

Metro has reported that the first noises came from Belarus in 2008, while in the same year ‘ear-defeaning’ sounds were posted to YouTube by an anonymous user.

According to Metro, NASA say it could be the earth’s ‘background noise’.

A statement from the agency said: ‘If humans had radio antennas instead of ears, we would hear a remarkable symphony of strange noises coming from our own planet. Scientists call them “tweeks,” “whistlers” and “sferics.”

"They sound like background music from a flamboyant science fiction film, but this is not science fiction. Earth’s natural radio emissions are real and, although we’re mostly unaware of them, they are around us all the time."

Trevor Farbo who posted a video from Queensland, Australia posted a video from when he was out for a walk.

He wrote, "We heard these strange noises, similar to what others have been hearing in other parts of the world, coming from the sky.

"It should be noted that storm clouds were rolling in at the time they were heard. Anyone have any idea of what could be causing this?"